The present invention relates to a channel selection method to be applied to a wireless communication system wherein a plurality of wireless channels are used by a plurality of wireless stations, each selected dynamically according to usage of the wireless channels checked by each of the wireless stations, and particularly relates to the channel selection method which enables a dynamic and appropriate channel selection even when but few available wireless channels are left to be selected.
In conventional connection-less wireless communication systems to be applied to a wireless LAN (Local Area Network), for example, such as described in "Wireless LAN Medium Access Control and Physical Layer Specifications", Draft Standard IEEE 802.11, P802.11D2.0, (July 1995), (hereafter called the first prior document), a wireless channel is commonly used by a base station connected to a wired network and one or more mobile stations connected with the base station for configuring a wireless link of a wireless communication system, and a wireless channel is fixedly assigned to each base station considering propagation characteristics and the traffic prediction of each base station. The mobile station designates a wireless channel assigned to a base station of a zone where the mobile station actually exists, manually or according to a control signal which is periodically or continuously transmitted from the base station.
However, when the wireless channels are assigned fixedly for each of the base stations according to the propagation characteristics and the traffic prediction, there may occur interferences between base stations whereto the same wireless channel is assigned, if the actual propagation characteristics or the actual communication traffic is changed from the prediction.
For dealing with this problem, we proposed a dynamic channel selection method in a paper entitled "A Proposal of Packet DCA for a Wireless LAN System", B-652, p. 136, Proceedings of the Communication Society Congress 1996, IEICE, (hereafter called the second prior document), wherein an appropriate channel selection according to actual propagation characteristics and communication traffic is realized by enabling a wireless station to select a wireless channel not used by other wireless stations dynamically and independently, for establishing a new wireless link.
However, the channel selection method proposed in the second prior document is based on an assumption that a sufficient number of wireless channels are prepared so that there are always left some channels not used by other wireless stations and available for the new wireless link to be established, and there is no description concerning the case where no available channel is left unused. Therefore, there may arise wireless links whereto any wireless channel can be assigned, when the number of available wireless channels is insufficient.